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Osler Journal Club: The Cohort Study

Gu et al. NEJM 2009; 360 (2): 150-9

,Esteemed Moderator: J. Hunter Young, MD MHS

Discussants: Janice Leung, MD Chris Kanakry, MS3

Peter Leary, MD Michael Grunwald, MD

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e o or u y

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the basis of exposure

development of outcome

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Generic Pros and Cons of the

ohort tudy

Time based study allowsspeculation of causality (Note

Expensive Time consuming and vast

control)

Observational nature allows

Not randomized/clean

(i.e. toxic exposures often

group together and health care

Can study multiple outcomes

of a specific exposure

Not good for rare diseases or

outcomes with a long natural

Can Study rare exposures Attrition

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Why China why smoking why

this article?While smoking is on the decline in the

western world, the smoking epidemic isin the early stages in developing countries.

tobacco has been described as the #1

public health issue/crisis in China, but the

screening and populations is still not fullyknown.

about smoking as a whole, the authorssought to apply a much needed filter of

.

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carried out in all 30 provinces Multi-stage design of random cluster sampling

designed to get a nationally representative sample of

the Chinese general population > 15 yo .

1999-2000 follow-up study

study subjects

2 provinces did not have smoking data

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15 remaining provinces were evenly distributed in

eren geograp c reg ons an represen e var ouslevels of economic development in China

15 included provinces were similar to 15 excludedprov nces: Age: 55.9 yo vs. 55.3 yo

High school education: 24.0% vs. 23.4% . . .

Physical inactivity: 37.0% vs. 36.6%

Cigarette smoking history: 37.9% vs. 36.7%

, 76,134 men, 78,997 women 144,088 (92.9%) successful follow-up and inclusion in study

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Single clinic visit by physician or nurse

Standardized methods with stringent quality control

Standard questionaire to gather data on demographic

characteristics, medical history, and lifestyle risk

Tobacco smoking definition: 1 cig/day x 1 year

Height, weight, BMI, three BP measurements, work

related physical activity all assessed

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- 1999-2000 follow-up

Tracked subjects or next-of-kin to current address

In-depth interviews to ascertain disease status and informationregarding health/death

,

For deaths: information obtained from others:

Family (75%), PCP (12.6%), Other health care providers (3.8%),Employers, relatives, or friends (8.5%)

If patient died in hospital, MR obtained including: Medical history, PE, labs, autopsy findings, final diagnosis

Photocopies made of selected sections of medical records

,from family or health care provider

98.6% of deaths were verified by death certificate and/or medicalrecords

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- -

Reviewed medical history information anddeath certificates to determine final underlyingcause of death with prespecified criteria

Two committee members indepedently verified

Discrepancies adjudicated by discussion involvingadditional committee members

Committee members blinded to subjects smokinghistory and other baseline characteristics

Causes of death coded accordin to ICD-9

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ethics committee at Cardiovascular

Written informed consent obtained from all-

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Age-standardized mortality was calculated- -

mortality and age distribution of the

Chinese population using 2000 censusdata

Relative risks calculated for subjects who

had ever smoked compared with lifelongnonsmokers as reference

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- -

for a variety of covariables: Baseline age, level of education, alcohol

consumption, level of physical activity, presence of

hypertension, being overweight, self-reported

, ,

urbanization

Dose-response relationship of smoking

measured by stratifying smokers into 3 groups: 30.3 PYH

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Multivariable-adjusted relative risks of death associated

with smoking were obtained stratified by level ofurbanization (urban vs. rural), sex, and age (40-54, 55-64, 65 These estimates used to calculate the population attributable risk

(PAR) and 95% CIs for each subgroup using the following

standard equation (P = proportion of smokers, RR = relativer s :

PAR = (P x [RR-1] (P x [RR 1] + 1)

Overall relative risks or population attributable risks of death

the Chinese population in 2005

All p-values were two-sided and not adjusted for multiple

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Results

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Baseline Characteristics

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Dose-Related Response

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Population Attributable Risk

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Disease-Specific Risk

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Conclusions

e resu s o s s u y nvo v ng anationally representative sample of

smoking is a major preventable cause.

There was a significant, dose-

-years smoked and death.

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Conclusions

e num er o ea s a r u a e osmoking was much greater among

.

Lung cancer was the leading cause of.

COPD was the leading cause of death

r u w .

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Discussion

esu s are rou esome ecause e

prevalence of tobacco smoking has

in China.

in China has been dropping during

.

Chin Med J (Engl) 1987; 100:886-92.

Zhonghua Liu Xing Bing Xue Za Zhi 2005; 26:77-83

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Discussion

n e s u es n es ern

populations, this study shows that the

were similar among former and.

Smoking cessation has been relatively

. Most smokers quit because of chronic

.

JAMA 2008; 299:2037-47

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Discussion

risk associated with smoking than did

The magnitude of the relative risks

robabl reflects the lower numbersof cigarettes smoked in the past andthe later age of smoking initiation in

u urr y y rsmoking-related diseases.

Tobacco control policy analysis in China: economics and health.

Singapore: World Scientific Publishing 2008: 13-31.

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Study Limitations

by questionnaire, there may have

smoking exposure.

Hos ital records were available for71% of subjects who died.Therefore, the classification of cause

y ur rsubjects without hospital records.

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Study Limitations

e mor a y o ow-up was

conducted during the 1990s, which

and disease burden at that time.

- ,cancer and cardiovascular disease,

death in China. Therefore, the studyma underestimate current deathsattributable to smoking.

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Study Limitations

esp e e a us men or severa

potentially confounding factors in the,

nonsmokers may still differ with

contribute to disease risk.

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Study Limitations

e au ors es ma e e num er o

deaths attributable to smoking, not

prevented by smoking cessation.

exposure to smoking.